The present invention relates to vehicles such as lawn and garden tractors and riding lawn mowers used in the lawn and garden industry, particularly lawn mowers of the zero turn radius variety which include hydrostatic transaxles and which are steered by controlling the speed and direction of the ground-engaging drive wheels of the mower.
Zero turn radius mowers have long been favored by landscape maintenance professionals for their high level of maneuverability, because such mowers may be turned in place through 360xc2x0, allowing faster lawn cutting times. Such mowers are provided with a pair of reversible drive wheels, one on each side of the mower, which are independently controlled. Each wheel is driven by a separate fluid motor, and each motor is driven by a separate, positive displacement fluid pump. Normally, a gear reduction set is provided between the motor and each wheel, by which the speeds of the wheels are reduced, and their output torque increased. An engine, which is typically mounted to the frame of the mower, drives the pumps at constant speed, and the speed and direction of rotation of each wheel motor is individually controlled by altering the displacement of the associated pump and selecting which of two conduits through which fluids may flow from the pump to the motor. Rotation of the drive wheels in opposite directions at common speeds will spin the mower in place relative to the ground, thereby providing a zero turn radius.
A fluid pump and motor pair may be comprised of separate pump and motor units in fluid communication through hydraulic fluid lines. The axle and gear reduction set may include a separate unit attached to the motor unit. A separate pump and motor pair are required for driving each axle, as well as a separate fluid reservoir sump to provide any needed hydraulic fluid to the pump. Space on the mower must also be provided for packaging the reservoir or sump.
It is necessary that the engine and pump positions, and the motor and drive axle positions, be fixed relative to each other. Previous zero turn radius mowers rely on a mower frame, which may be made of heavy gauge sheet steel, plate steel, and/or angle iron, to provide structural rigidity not only between the engine and the pump units, but also between the two wheel motor units. To provide such rigidity, the frame may require substantial bracing and further, such frames must be provided with closely toleranced mounting holes for mounting the engine, as well as the individual pumps, motors, and gear reduction units. Thus, previous zero turn radius motors require a frame which is heavy, rigid, and expensive.
It is known in the art to provide a hydrostatic transmission module, in which a fuel pump and motor pair are located in a common housing. Further, the hydrostatic transmission module and an axle drive assembly may be attached together and shipped as a unit to a tractor or mower manufacturer. Examples of such hydrostatic transmission modules, and hydrostatic transaxles comprising such modules, are described in pending U.S. Pat. No. 6,301,885, and U.S. patent applications Ser. Nos. 09/498,692, filed Feb. 7, 2000, and Ser. No. 09/671,796, filed Sep. 27, 2000, all of which are assigned to Tecumseh Products Company, the disclosures of which are expressly incorporated herein by reference.
However, even though hydrostatic transmission modules and axle drive assemblies are available which are attached together and shipped as a package unit to a tractor or mower manufacturer, the assembly of same to the mower frame, followed by the separate assembly of the engine and the drive linkage components to the mower frame, add further expense and difficulty to manufacturing the mower.
Also known in the art are hydrostatic axle drive units in which a fluid pump and motor pair are be packaged with gear reduction means and a portion of an axle shaft in a common housing. One example of such an axle drive is Model 310-1400 IZT (Integrated Zero-Turn) transaxle manufactured by Hydro-Gear of Sullivan, Ill. One IZT transaxle unit is attached to each side of the mower, and drives one of the two drive wheels.
Separate axle drive units such as the IZT transaxle are rather large, and occupy a considerable amount of space on the mower. Further, separate axle drive units such as the IZT transaxle still rely on the mower frame to provide structural rigidity between the two axle drive units. Thus a heavy, rigid and expensive frame is still required to accommodate a pair of individual axle drive units such as IZT transaxles. Additionally, two of these large axle drive units must be shipped, stored and inventoried by the mower assembler.
What is needed is a compact powertrain module for zero turn radius mowers, which includes existing hydrostatic transmission module and axle drive assembly packages, and which also has built-in structural rigidity to accommodate a lighter and less expensive frame than would otherwise be necessary, thereby facilitating an easier and less costly zero turn radius mower assembly process, and reducing shipping and inventory administration costs for the manufacturers of such mowers.
The present invention provides a powertrain module for a zero turn radius vehicle, such as a tractor or mower, the powertrain module generally including a mounting plate to which an engine, a pair of hydrostatic transmission modules, and a pair of axle drive units are attached to form a self-contained powertrain module which may be shipped as a single packaged unit to the mower assembler for installation into the zero turn radius implement. The hydrostatic transmissions and axle drive units may be respectively attached to one another as hydrostatic transmission/axle drive unit pairs.
The mounting plate provides structural rigidity between the powertrain components attached thereto. Therefore, the powertrain module may be attached directly to the frame of the implement, or alternatively, the powertrain module may itself serve as a structural frame member for the implement, wherein the mounting plate of the powertrain module cooperates with other structural members of the implement to define the implement frame. The powertrain module may additionally include other components such as brake assemblies, ground-engaging wheels, drive linkage between the engine and the hydrostatic transmissions, or other components, if desired.
Advantageously, the powertrain module may be custom designed and assembled by a powertrain manufacturer to meet the particular specifications of an original equipment manufacturer (OEM), and may be shipped to the OEM as a single packaged unit for easy drop-in assembly into a zero turn radius mower. Further, integration of the engine, hydrostatic transmissions, and axle drive units into a single, self-contained modular assembly obviates the need to separately attach each of the foregoing components to a frame, thereby reducing the cost and complexity of the frame, as well as the difficulty of assembling the implement.
In one form thereof, the present invention provides a self-contained powertrain module including a structural member, an engine attached to the structural member, and first and second hydrostatic transmission modules connected to the structural member. Each hydrostatic transmission module includes a transmission housing, and a rotating fluid pump and a rotatable fluid motor disposed within the housing. Each pump is driven by the engine and is of variable displacement, and each motor is rotated at various speeds and in forward and reverse directions in response to changes in its associated pump""s displacement. The inventive module further provides first and second axle drive units connected to the structural member. Each axle drive unit includes a housing and a speed reduction gear train disposed therein. Each speed reduction gear train has an input and an output, the first hydrostatic transmission module motor being operably coupled to the first axle drive unit gear train input, the second hydrostatic transmission module motor being operably coupled to the second axle drive unit gear train input. First and second axles are respectively operably coupled to the first and second gear train outputs, and respectively extend through the first and second axle drive unit housings.
In another form thereof, the present invention provides a zero turn radius vehicle which includes a first frame portion and a second frame portion, the latter including a powertrain module separably attached to the first frame portion. The powertrain module includes a substantially rigid structural member attached to the first frame portion, an engine attached to the structural member, and first and second hydrostatic transmission modules connected to the structural member. Each hydrostatic transmission module includes a transmission housing, and a rotating fluid pump and a rotatable fluid motor disposed therein. Each pump is of variable displacement and is in driving relationship with the engine, and each motor is in fluid engagement with its associated pump, each motor being rotated at various speeds and in forward and reverse directions in response to changes in pump displacement. First and second axle drive units are connected to the structural member, and each axle drive unit includes a housing and a speed reduction gear train disposed within the axle drive unit housing, each the speed reduction gear train having an input and an output. The first hydrostatic transmission module motor is operably coupled to the first axle drive unit gear train input, and the second hydrostatic transmission module motor is operably coupled to the second axle drive unit gear train input. First and second independently rotatable axles are respectively operably coupled to the first and second gear train outputs, and respectively extend through the first and second axle drive unit housings. A ground-engaging wheel is attached to each axle.